Kindergarten student Tianna Swisher attempts to drink from the water fountain at Montour Preserve, near Washingtonville, Pa., during the school's outdoor field trip. Fluoride in drinking wate may now be too much of a good thing. A reported increase in the spotting problem is one reason the federal government will announce it plans to lower the recommended limit for fluoride in water supplies.

ATLANTA (AP)  Fluoride in drinking water — credited with dramatically cutting cavities and tooth decay — may now be too much of a good thing. Getting too much of it causes spots on some kids' teeth.

A reported increase in the spotting problem is one reason the federal government will announce Friday it plans to lower the recommended levels for fluoride in water supplies — the first such change in nearly 50 years.

About 2 out of 5 adolescents have tooth streaking or spottiness because of too much fluoride, a surprising government study found recently. In some extreme cases, teeth can even be pitted by the mineral — though many cases are so mild only dentists notice it.

Health officials note that most communities have fluoride in their water supplies, and toothpaste has it too. Some kids are even given fluoride supplements.

The U.S. Department of Health and Human Services is announcing a proposal to change the recommended fluoride level to 0.7 milligrams per liter of water. And the Environmental Protection Agency will review whether the maximum cutoff of 4 milligrams per liter is too high.

The standard since 1962 has been a range of 0.7 to 1.2 milligrams per liter.

The Centers for Disease Control and Prevention reports that the splotchy tooth condition, fluorosis, is unexpectedly common in kids ages 12 through 15. And it appears to have grown much more common since the 1980s.

"One of the things that we're most concerned about is exactly that," said an administration official who was not authorized to speak publicly before the release of the report. The official described the government's plans in an interview with The Associated Press.

The government also is expected to release two related EPA studies which look at the ways Americans are exposed to fluoride and the potential health effects. This shift is sure to re-energize groups that still oppose it.

Fluoride is a mineral that exists naturally in water and soil. About 70 years ago, scientists discovered that people who lived where water supplies naturally had more fluoride also had fewer cavities. Some locales have naturally occurring fluoridation levels above 1.2. Today, most public drinking water supplies are fluoridated, especially in larger cities. Counting everyone, including those who live in rural areas, about 64% of Americans drink fluoridated water.

Maryland is the most fluoridated state, with nearly every resident on a fluoridated water system. In contrast, only about 11% of Hawaii residents are on fluoridated water, according to government statistics.

Fluoridation has been fought for decades by people who worried about its effects, including conspiracy theorists who feared it was a plot to make people submissive to government power.

Those battles continue.

"It's amazing that people have been so convinced that this is an OK thing to do," said Deborah Catrow, who successfully fought a ballot proposal in 2005 that would have added fluoride to drinking water in Springfield, Ohio.

Reducing fluoride would be a good start, but she hopes it will be eliminated all together from municipal water supplies.

Voters in Springfield, which is near Dayton, turned down the measure 57 to 43% in 2005. They also rejected the idea in the 1970s.

Catrow said it was hard standing up to city hall, the American Dental Association and the state health department. "Anybody who was anti-fluoride was considered crazy at the time," she said.

Drinking water patterns have changed over the years, so that some stark regional differences in fluoride consumption are leveling out. There was initially a range in recommended levels because people in hotter climates drank more water. But with air conditioning, Americans in the South and Southwest don't necessarily consume more water than those in colder states, said one senior administration official.

Fluorosis is considered the main downside related to fluoridation.

According to the CDC, nearly 23% of children ages 12-15 had fluorosis in a study done in 1986 and 1987. That rose to 41% in the more recent study, which covered the years 1999 through 2004.

"We're not necessarily surprised to see this slow rise in mild fluorosis," Dr. William Kohn, director of the CDC's division of oral health, said in a recent interview.

Health officials have hesitated to call it a problem, however. In most kids, it's barely noticeable; even dentists have trouble seeing it, and sometimes don't bother to tell their unknowing patients. Except in the most severe cases, health officials considered the discoloring of fluorosis to be a welcome trade-off for the protection fluoride provides against cavities.

Generally, the prevalence of tooth decay in at least one tooth among U.S. teens has declined from about 90% to 60%. Health officials call water fluoridation one of the ten greatest public health accomplishments of the last century.

"One of water fluoridation's biggest advantages is that it benefits all residents of a community — at home, work, school, or play. And fluoridation's effectiveness in preventing tooth decay is not limited to children, but extends throughout life, resulting in improved oral health," said HHS Assistant Secretary for Health Dr. Howard Koh, in a statement.

The government is not suggesting people change their brushing or other tooth-care habits.

The American Dental Association on Friday morning released a statement applauding the government announcement.

"This is a superb example of a government agency fulfilling its mission to protect and enhance the health of the American people," said ADA President Dr. Raymond F. Gist, DDS.

Indeed, many health leaders continue to be worried about cavities, particularly among poor families with kids who eat a lot of sweets but don't get much dental care. The American Public Health Association in November adopted a resolution calling for coordinated programs to be established at public health, dental and medical clinics to offer fluoride varnish — a highly concentrated lacquer painted on teeth to prevent cavities.

Secretary Kathleen Sebelius could make a final decision within a few months, the administration official said.

There is no fluoride in most European water supplies. In Britain, only about 10% of the population has water with fluoride in it. It's been a controversial issue there, with critics arguing people shouldn't be forced to have "medical treatment" forced on them. In recent years, the UK has tried to add fluoride to communities with the worst dental health but there's still considerable opposition.

Some European nations used to add fluoride to water supplies but have stopped. Some countries add it to salt instead.

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